User blog comment:Zadude/Anybody recognize the song from this part?/@comment-3359571-20140217002538

I think is "Synapse no Sekai", but take a look here:

http://soranootoshimono.wikia.com/wiki/Sora_no_Otoshimono_Forte_-_Heart_Ga_Me_wo_Samasu_Ongakushu